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What is intermittent fasting?

Intermittent fasting is a type of diet regimen that gained a lot of attention in the health and fitness industry. People practise it for various purposes including weight loss, improve their health and religious purposes. As opposed to other diet regimens that focus on what to eat and what to avoid, intermittent fasting focuses on when to eat. It is a practice of regular intervals between fasting and feeding cycles where you only eat during your feeding period. During the fasting period, there is complete abstinence from food, while consuming zero-calorie drinks are still permitted such as black coffee, tea, water. It is based on the idea that after a prolonged period without food intake, the body will run out of its sugar store and turn to burn fats for energy, which is referred to as metabolic switching. Some studies showed that intermittent fasting may offer several health benefits such as weight loss, better blood sugar control, and reduced heart disease risk.

How is it being done?

There exist different methods of intermittent fasting, however, all of them are governed by the same underlying principle that involves splitting the day or week into fasting and feeding period. The different forms of intermittent fasting include:

  1. Time-restricted feeding (TRF): limiting food intake to a set period of time in a day, such as the 16/8 fasting that involved fasting for 16 hours and eating for the remaining 8 hours. This method is a good place to start for a beginner as it is easy to follow.
  2. Periodic feeding (PF): fast for 2 days a week, usually consume 500-600 calories during fasting day while eating normally in the remaining days of the week. 
  3. Alternate day fasting (ADF): 24 hours fast or consuming only 25% calorie during the fasting day, followed by 24 hours of non-fast, such as eat-stop-eat where people can eat as much as they want during feeding day. This method is quite extreme and may not be suitable for beginners. 
  4. Ramadan fasting (RF): usually done for religious purposes, it is a time-restricted feeding where food consumption is only permitted during nighttime. 

What is the scientific evidence on intermittent fasting?

Due to the increasing popularity of intermittent fasting, many studies were being performed to assess the effectiveness of intermittent fasting on weight loss and other health outcomes. 

Weight loss

Almost any form of intermittent fasting has shown to be effective for short-term weight loss. A systematic review in 2020 with a total of 944 participants had shown that the weight loss effect of intermittent fasting ranged from 0.8%-13.0% from their initial body weight with no adverse events being reported. The effect of weight loss from intermittent fasting was comparable to the conventional calorie restriction diet. 

 

Blood sugar control 

Intermittent fasting was shown to be effective in reducing fasting glucose and insulin resistance and it might be attributed to the reduction in body weight and body fats. A clinical trial performed among 137 diabetic adults showed that the intermittent energy restriction group was able to achieve a similar HbA1c reduction as the continuous energy restriction group. Intermittent fasting may be promising in the future to be used as a complement to better diabetic control, however, the patients should consult their doctors before beginning an intermittent fasting regimen.

 

Cardiovascular risk

Intermittent fasting was shown to significantly reduce systolic blood pressure, LDL-cholesterol, triglycerides, and increase HDL. However, the latest systematic review published in 2021 is not able to substantiate the cardioprotective effect of intermittent fasting as the available evidence is of low quality.  

The pitfalls of intermittent fasting

Even with the weight loss benefits and other health improvements from intermittent fasting, this diet regimen is not necessarily suitable for everyone and there are potential pitfalls that we need to watch out for.

a. Looking at the long term

Most of the beneficial effects were shown in the short term practice of intermittent fasting. The question is: Can these benefits be sustainable in the long run? How to make sure long term adherence to this diet regimen? Looking at these beyond 3, 5 and even 10 years. 

b. Not suitable for every group

There are some groups of individuals that need to steer clear from practising intermittent fasting. This includes children under 18 years old, pregnant and breastfeeding mothers, people with certain medical conditions such as diabetes, and people with a history of eating disorders.

c. Overcompensation

Human nature has a tendency to reward ourselves after a long period of hard work. The concern here is people might be overeating during their feeding phase after a long period of starvation (fasting phase). This bingeing behaviour may lead to weight gain and even negatively affecting their health.

d. Compliance 

The side effects that may be experienced during the fasting phase include dizziness, headache, irritability and nausea might contribute to the dropout. Furthermore, people who are habitually eating or snacking throughout the day might find it difficult to stick to this diet regimen. 

References 

Allaf, M., Elghazaly, H., Mohamed, O.G., Fareen, M.F.K., Zaman, S., Salmasi, A.-M., Tsilidis, K., and Dehghan, A., 2021. Intermittent fasting for the prevention of cardiovascular disease. Cochrane Database of Systematic Reviews, 2021 (1).

Carter, S., Clifton, P.M., and Keogh, J.B., 2018. Effect of intermittent compared with the continuous energy-restricted diet on glycemic control in patients with Type 2 Diabetes: a randomized noninferiority trial. JAMA Network Open, 1 (3).

CS, D., RE, C., SN, C., KN, R., RE, W., CE, R., CE, H., and L, R., 2016. Intermittent energy restriction and weight loss: a systematic review. European journal of clinical nutrition, 70 (3), 292–299.

Dong, T.A., Sandesara, P.B., Dhindsa, D.S., Mehta, A., Arneson, L.C., Dollar, A.L., Taub, P.R., and Sperling, L.S., 2020. Intermittent Fasting: A heart-healthy dietary pattern? The American journal of medicine, 133 (8), 907.

Ganesan, K., Habboush, Y., and Sultan, S., 2018. Intermittent fasting: the choice for a healthier lifestyle. Cureus, 10 (7).

Mohsen, N., Maryam, A.-N., Masoud Mahdavi, R., Mostafa, M., Seyedeh Sania, S., Saeed, A., Maryam, S., Seyed Amir, M., Neda, S., Mohsen, M., and Abdolzera, N., 2012. Effects of Ramadan fasting on cardiovascular risk factors: a prospective observational study. Nutrition Journal, 11 (1), 11–69.

Welton, S., Minty, R., O’Driscoll, T., Willms, H., Poirier, D., Madden, S., and Kelly, L., 2020. Intermittent fasting and weight loss: Systematic review. Canadian Family Physician, 66 (2), 125.

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